This invention relates to a pulse signal generating device for a tape recorder, and more particularly to a pulse signal generating device for optically detecting the number of revolutions or the speed at which a shaft of a tape recorder rotates.
Generally, a tape recorder needs a device which optically detects the number of revolutions or speed of rotation of reel shafts so that an automatic shut-off or an electronic counter, for example, may be timely driven. Known as such a device is a pulse signal generating device which has a direct light-transmitting type photo-coupler. The pulse signal generating device, however, is expensive and is large, thus occupying a large space. Another device known and used as such is a pulse generating device which has a hole element for detecting changes in magnetic field intensity that occur as a rotary member having a magnet rotates together with reel shafts. To manufacture this pulse signal generating device it is necessary to magnetize a portion of the rotary member and to embed a magnet in a portion of the rotary member. These steps require many man-hours, and the device is inevitably expensive.